Law enforcement in California, and throughout the United States, will now
generally need a search warrant to track cellphone location data after
a U.S. Supreme Court ruling on June 22 dealing with privacy rights in
the digital era.

Justices ruled 5-4 that the cellphone location information used to convict
Timothy Carpenter of armed robbery is subject to the Fourth Amendment
protection of the U.S. Constitution. Chief Justice John Roberts and the
court’s four liberal justices were part of the majority, while the
court’s other four conservatives dissented.

Cellphone data is often used by law enforcement agencies in criminal cases.
Though the “third-party doctrine,” the FBI gained access to
the records with a court order that requires a lower standard than the
“probable cause” needed for a warrant.

In all, law enforcement collected 12,989 location points cataloging Carpenter’s
movements over a period of 127 days. These points placed him near four
of the robbery locations at the time they happened.

The justices ruled that the third-party doctrine does not apply to cellphone
location information, empathizing that individuals reasonably expect that
this type of information will remain private. Since cellphones automatically
transmit location information and are a ubiquitous and required party
of life in today’s society, users do not give up their rights to
keep their location data private simply because their cellphone carrier
also has the data.

However, the ruling failed to address other digital privacy battles, such
as whether police need warrants to access real-time cellphone location
data to track criminal suspects. It is limited to cellphone tracking information
and does not affect other business records, including those held by financial
institutions.

This ruling was the third in recent years in which the Supreme Court has
ruled against law enforcement in major cases involving criminal law and
new technology. In 2014, it decided that police generally need a warrant
to search an individual’s cellphone content upon arrest. Two years
before, it ruled a warrant is required to put a GPS tracking device on
a vehicle.

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